1. Field of Invention
This invention relates to biodegradable paper-based laminates and methods for making biodegradable paper-based laminates.
2. Description of the Related Art
Paper-based laminates commonly include a substrate of paperboard, container board, or other form of paper. Due to paper's inherent limitations relative to its porosity to deleterious liquids or gases, its physical properties such as tear resistance, and other limitations for packaging uses, the paper-based substrate is coated or laminated with one or more layers of polymeric materials, which are selected to obviate one or more of the limitations of the paper-board as a packaging material. These polymeric materials such as, but not limited to, low-density polyethylene (LDPE), nylon, polyethylene terephthalate (PET), and ethylene vinyl alcohol copolymer (EVOH) are not generally considered biodegradable. Paper-based laminates are useful in the formation of packaging for a large variety of products. Such packaging is commonly used once or a minimal number of times and then disposed. The volume of usage of such laminates has created potential problems with respect to their biodegradability in landfills, etc. Uses of paper-based laminates include packaging for food products (liquids, solids, hot or cold), ream wrap, sandwich wrap, and a myriad of other uses.
Paper-based laminates for food service uses are typically extrusion coated with low-density polyethylene (LDPE) or other similar polymer(s) in order to hold liquids for a longer period of time without leaking or becoming soft as is common with 100% paper cups. For example, cups for hot beverages such as coffee generally have a layer of LDPE on the inside for liquid resistance and sealing. Cold drink cups for soft drinks and the like are typically coated with LDPE on both sides to prevent condensation that forms on the outside of the cup from softening the paper. LDPE coat weights of 0.5-1.5 mils (7.2-21.6 lb/3000 ft2) are common.
Many paper-based laminates are used in disposable packaging once or a very minimal number of times then disposed. The LDPE coating is not readily biodegradable, and therefore, the cup might remain in a landfill for many years without degrading. The use of one or more biodegradable polymers instead of LDPE is desirable to render the used cups more “environmentally friendly”.
Paper-based laminates for food service uses are typically extrusion coated with low-density polyethylene (LDPE) or other similar polymers in order to hold liquids for a longer period of time without leaking or becoming soft, as is common with 100% paper cups. For example, cups for hot beverages such as coffee generally have a layer of LDPE on the inside for liquid resistance and sealing. Cold drink cups for soft drinks and the like are typically coated with LDPE on both sides to prevent condensation that forms on the outside of the cup from softening the paper. LDPE coat weight of 0.5-1.5 mils (7.2-21.6 lb/3000 ft2) are common.
In addition to cups, other coated paper products such as gable-top cartons, folding cartons, corrugated boxes, paper pouches, sandwich wraps, and ream wrap may also benefit from including an environmentally friendly biodegradable material.
Renewable-resource-based polymers exist. These polymers produced from chemicals that can be grown. This allows for greater supply and price stability.
In addition, these materials are biodegradable and compostable. In Europe and Asia, where landfill space is very limited, compostable renewable-resource-based materials are preferred. In additional, municipal composting is a growing trend in North America, especially where landfills are filling too quickly and related costs are rising rapidly.
Compostable renewable-resource-based materials include polylactic acid (PLA) and polyhydroxyalkanoates (PHA).
Usually, “green” materials like PLA and PHA are difficult to process via extrusion because of their sensitivity to moisture and high temperatures.